1. Field of the Invention
The present invention relates to a concentricity control apparatus, and more particularly to a concentricity control apparatus for controlling a concentricity between a stator body and a rotor body in an induction motor.
2. Description of the Prior Art
Generally, a rotor assembly in an induction motor is rotated at a lower speed than a synchronous rotational speed by a rotary magnetic field induced at a stator assembly.
The induction motor includes a cylindrical core having a plurality of poles continuously formed therein, a stator assembly, a rotor assembly and a bearing.
In other words, when an electrical current applied to the stator assembly forms a rotary magnetic field at a predetermined number of poles, a certain electrical current is induced in the rotor assembly to rotate a rotor.
Particularly, a concentricity controlling induction motor disposed with a concentricity control apparatus such as an Active Magnetic Bearing AMB and the like is used for reduced generation of heat caused by rotation of the rotor assembly in the motor rotating at a high speed.
The AMB is treated in a paper authored on Jul. 4, 1996 by L. Scott Stephens and Carl R. Knospe, titled as "Effect of Magnetic Pole Arrangement on Core Loss in Laminated High-speed Magnetic Journal Bearing".
The concentricity control apparatus as illustrated in FIG. 5 is disposed with a rotary body 50, a stator body 52, a plurality of driving coils 54, a sensor 55 and an operation unit 56.
In other words, when a concentricity controlling induction motor is rotated by an operation circuit (not shown), the sensor 55 detects a position of the rotary body 50, that is, a concentric status of the stator body 52 and the rotor body 50.
At this time, an eccentricity of the rotor body 50 to one side is detected, transmitted to the operation unit 56, and then the eccentric position is transmitted to the driving circuit 53.
When the eccentricity is transmitted to the operation unit 56, a residual amount of current large enough to offset the eccentricity is supplied from the operation unit 56 to the respective driving coil 54 which is located at the eccentric position.
When an offsetting or correcting current is supplied to the respective driving coil 54, a correcting magnetic force is generated from a pole 51 and the driving coil 54, so that simultaneously the rotor body 50 is pushed to eliminate eccentricity.
Of course, in order to more accurately control the eccentricity of the rotor body 50, a good many poles, that is, a combination of respective poles 51 and driving coils 54 are needed and a very accurate driving circuit 53 is necessary to respectively control same.